72020b1901
Implements the walking skeleton from the roadmap: agents connect to one HTTP
endpoint and Nexus aggregates upstream MCP servers behind it with namespaced
tools. Written in Go (single static binary), no external services required.
What works end-to-end (verified live + hermetic e2e tests):
- MCP protocol layer: JSON-RPC 2.0 + initialize/tools.list/tools.call
(internal/mcp), with stdio (subprocess) and Streamable HTTP client
transports, and a reusable stream transport for in-process wiring.
- Router + Dynamic Tool Registry: connects/initializes upstreams in parallel,
loads tools, namespaces them as {namespace}.{tool}, dispatches tools/call to
the owning upstream; refreshes on list_changed. A failed upstream stays
not-ready without taking down the gateway (data plane stays up).
- Gateway: single MCP endpoint (POST /mcp) that is an MCP server to agents,
plus /healthz and a minimal /metrics exposition.
- CLI (cmd/nexus): `serve`, `connect` (stdio<->HTTP bridge for local agents),
`demo-mcp` (built-in zero-dep demo server: echo/add/now), `version`.
- Config: declarative YAML with env expansion + validation.
- Store: persistence interfaces + in-memory impl (SQLite lands later).
Foundations for later phases: domain types (ARCHITECTURE §7), two-plane
split, event-driven refresh seam.
Tooling: Makefile (build/test/vet/fmt with version ldflags), config.example
.yaml. GOPATH moved to /go so it doesn't collide with the module root at /root;
.gitignore whitelist extended to track Go sources while ignoring build output.
Tests: unit (registry/namespacing) + full e2e (client -> demo server over
pipes -> router -> HTTP gateway: initialize, aggregated tools/list, tool-call
routing, unknown-tool error). go vet + gofmt clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
65 lines
2.0 KiB
Go
65 lines
2.0 KiB
Go
// Package app wires configuration into the running control/data plane. In
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// Phase 1 it builds the Router from static upstream config; later phases feed
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// instances from discovery + the reconciler instead.
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package app
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import (
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"fmt"
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"log/slog"
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"os"
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"gitea.thetempleofdoom.com/drjones/mcp-gateway-nexus/internal/config"
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"gitea.thetempleofdoom.com/drjones/mcp-gateway-nexus/internal/domain"
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"gitea.thetempleofdoom.com/drjones/mcp-gateway-nexus/internal/mcp"
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"gitea.thetempleofdoom.com/drjones/mcp-gateway-nexus/internal/router"
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"gitea.thetempleofdoom.com/drjones/mcp-gateway-nexus/internal/version"
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)
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// nexusInfo identifies Nexus to upstream MCP servers.
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func nexusInfo() mcp.Implementation {
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return mcp.Implementation{Name: "mcp-nexus", Version: version.Version}
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}
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// BuildRouter constructs a Router with an upstream client per config entry.
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// Transports are created but not connected; call ConnectAll afterwards.
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func BuildRouter(cfg *config.Config, log *slog.Logger) (*router.Router, error) {
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r := router.New(nexusInfo(), log)
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for _, u := range cfg.Upstreams {
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transport, err := buildTransport(u)
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if err != nil {
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return nil, fmt.Errorf("upstream %q: %w", u.Namespace, err)
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}
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client := mcp.NewClient(transport, nexusInfo())
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r.Add(u.Namespace, client)
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}
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return r, nil
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}
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func buildTransport(u config.UpstreamConfig) (mcp.Transport, error) {
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switch domain.TransportKind(u.Transport) {
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case domain.TransportStdio:
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return mcp.NewStdioTransport(mcp.StdioConfig{
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Command: u.Command,
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Args: u.Args,
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Env: u.Env,
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Dir: u.Dir,
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Stderr: prefixWriter{ns: u.Namespace},
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})
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case domain.TransportHTTP:
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return mcp.NewHTTPTransport(mcp.HTTPConfig{
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Endpoint: u.Endpoint,
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Headers: u.Headers,
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})
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default:
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return nil, fmt.Errorf("unknown transport %q", u.Transport)
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}
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}
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// prefixWriter tags upstream stderr lines with their namespace on our stderr.
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type prefixWriter struct{ ns string }
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func (p prefixWriter) Write(b []byte) (int, error) {
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fmt.Fprintf(os.Stderr, "[upstream:%s] %s", p.ns, b)
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return len(b), nil
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}
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